Recently, with the reduction in weight and size of electrical appliances, development of a non-aqueous liquid electrolyte secondary battery having high energy density, for example lithium secondary battery, has been advanced. Also, as application field of lithium secondary battery is expanded, further improvement in its battery characteristics has been desired.
In this situation, a secondary battery based on metal lithium as anode electrode has been studied as a battery capable of achieving higher capacity. However, there is a problem that metal lithium grows as dendrite on repeated charges and discharges, and when this reaches the cathode electrode, shortings in the battery occurs. This has been the greatest obstacle in realizing a lithium secondary battery based on metal lithium as anode electrode.
On the other hand, a non-aqueous liquid electrolyte secondary battery has been proposed, in which carbonaceous material capable of intercalating and deintercalating lithium, such as coke, artificial graphite or natural graphite, are used for the anode electrode in place of metal lithium. In such a non-aqueous liquid electrolyte secondary battery, growth of metal lithium as dendrite can be avoided and battery life and safety can be improved. When graphite of these kinds are used as anode electrode, capacity is known to be usually of the order of 300 mAh·g−1, 500 mAh·cm−3.
Recently, proposals have been made for the anode electrode active material based on simple metal element capable of forming an alloy with lithium such as Si, Sn and Pb, an alloy containing at least one of these metal elements, or metal compound containing these metal elements (hereafter referred to as “anode electrode active material containing Si, Sn, Pb and the like”, as appropriate). The capacity of these materials per unit volume is of the order of 2000 mAh·cm−3 or larger, which is about 4 times or even larger than that of graphite. Therefore, higher capacity is obtained by using these materials.
Although a secondary battery using anode electrode active material containing Si, Sn, Pb and the like is suitable for realizing higher capacity, there is a decrease in safety, and anode electrode active material deteriorates on repeated charges and discharges, leading to reduced charge-discharge efficiency and deterioration of cycle characteristics.
Therefore, in order to secure safety and prevent a decrease in discharge capacity, a proposal has been made to include cyclic carbonate ester or a polymer of carbonate ester and phosphoric acid triester in the non-aqueous liquid electrolyte used for a secondary battery (Patent Document 1). Furthermore, a proposal has been made to add, in the non-aqueous liquid electrolyte, a heterocyclic compound having sulfur atom and/or oxygen atom in the ring structure and to form a protective layer on the surface of the anode electrode active material, thus improving charge-discharge cycle characteristics (Patent Document 2).
Furthermore, for a non-aqueous liquid electrolyte secondary battery based on various anode electrode material, a liquid electrolyte was proposed to which various compounds are added in addition to its electrolyte and main solvent, in order to improve such characteristics as load characteristics, cycle characteristics, storage characteristics and low-temperature characteristics.
For example, in order to suppress decomposition of liquid electrolyte of a non-aqueous liquid electrolyte secondary battery based on graphite anode electrode, a carbonate derivative having an unsaturated bond has been proposed such as an liquid electrolyte containing vinylene carbonate and its derivative (for example, Patent Document 3), or a liquid electrolyte containing ethylene carbonate derivative having non-conjugated unsaturated bond in its side chain (for example, Patent Document 4).
In the liquid electrolyte containing these compounds, the above-mentioned compounds are reduced and decomposed on the surface of the anode electrode and a protective layer is formed, which inhibits excessive decomposition of the liquid electrolyte. A halogen-containing carbonate was also proposed for the same purpose (for example Patent Document 5).
[Patent Document 1] Japanese Patent Application Laid-Open Publication No. H11-176470
[Patent Document 2] Japanese Patent Application Laid-Open Publication No. 2004-87284
[Patent Document 3] Japanese Patent Application Laid-Open Publication No. H8-45545
[Patent Document 4] Japanese Patent Application Laid-Open Publication No. 2000-40526
[Patent Document 5] Japanese Patent Application Laid-Open Publication No. H11-195429